I hope that in 809C - Find a car you aren't talking about thing that the value in cell (i, j) is (j - 1)xor(i - 1) + 1... If you are, then you should read about Sprague Grundy theorem. If you are talking about that recursion, then you should read about how xor behaves. I can bet that most of participans didn't write brute force to this problem, it's well known that this matrix behaves like this. If it comes to problem 815B - Karen and Test, then yes, it isn't the most interesting sort of problems, but imo it's not so bad on individual contests, where you have computer just for yourself and brute force is easy to implement and gives much.

Seems you got aggressive after getting up to top 10 :( (Yeah rating changes people)

Anyway, it's a programming contest, I can bet that most of participants would write a brute and recognize the pattern for 5 minutes rather than thinking for > 10 minutes of an interesting solution and fapping after getting the idea. I bet most people fap after getting higher rating more frequently than after getting nice ideas (However I'd fap for nice ideas)

Problems alike shouldn't exist in my opinion in a CF round (This comment will be downvoted because you are who you are and I am just a normie but I don't care), It make some get what they may not deserve.

Huh, hold on, your comment looks much more aggresive to me :P. As for me and find a car — I knew that it is i^j with some +-1 instant I saw that picture, I already encountered exactly same matrix at least 3 times and it is not hard to come up with it from scratch (smallest integer not present in some set — sounds pretty familiar, probably has some connection with games theory, xors etc). However I was not able to solve the problem even though I spent a long time on it. As for today's problem, yes, I agree it is kind of problem when you need to write a bruteforce to notice the pattern but I think such problems are completely fine, especially on individual contests.

I really hate that situation when you sit and boost your brain to come up with an idea. I tried some binomial shit today (but seems I am not experienced enough), anyway in the end couldn't come up with something. But when most of people wrote that it was patterns stuff I was pretty much like

and BTW this post was just for fun and mentioning the notorious coincidence but seems your friend has been so much serious recently :D I hope he hasn't been friendzoned

I would say I am rather experienced with binomials and shit but I would say there was no way to concluding how does it look like without writing bruteforce. Problems like that happen from time to time, it is not something extraordinary.

I think brute-forcing is just another idea to try during contest, neither better, nor worse.

However, my way to find the solution was to draw some pyramids for some short sequences like a b c, a b c d. When you notice a+c b+d in the third row of pyramid beginning with a b c d, you can smell something interesting, when you extend the first row with e f then magically a+2c+e b+2d+f in the fifth row appears, you can continue that process, prove it or start believing it works and code it. Some may say that it's essentialy brute-forcing but it shows that this problem really can be solved without using PC, which could be important during team competitions (for example your teammates have some easier problems to code in the first hour).

Sometimes solving small cases can help you understand the structure of the problem better ;)